Technical Field
The present invention relates to a digital acoustic system using a digital speaker apparatus which directly converts a digital signal into analog audio and applications thereof.
Description of Related Art
Digital speaker technology to directly convert a digital signal into analog audio has been proposed (for example, refer to WO 2007/135928).
A method of directly converting analog audio using a circuit which is input with two digital signals X (L) and Y (R) and which outputs a plurality of digital signals by ΔΣ-modulator and a mismatch shaping filter circuit wherein a plurality of speakers or a plurality of elements are driven by the plurality of digital signals is shown in FIG. 22 of Patent Document 1.
This type of digital speaker apparatus using digital speaker technology which directly converts a digital signal into analog audio has smaller power consumption compared to an analog speaker apparatus driven by an analog electric signal. In addition to this, since this type of digital speaker apparatus uses a plurality of speaker elements or a plurality of driving elements (such as coils), it is possible to output a large sounds compared to a conventional single speaker or a speaker that uses a single drive element.
However, in a digital speaker apparatus a circuit that outputs a plurality of digital signals using a digital signal from a PCM sound source using a ΔΣ-modulator and mismatch shaping filter circuit is essential and it is necessary to use a fine digital process to implement the circuits on an LSI.
FIG. 1 shows a conventional example of a digital speaker apparatus system as a typical example of a digital acoustic system using a conventional digital speaker apparatus. This conventional digital speaker apparatus system is composed of a circuit for outputting a plurality of digital signals by a ΔΣ-modulator, a post-filter circuit, and a plurality of speaker driving elements. A one bit digital input signal (110) is input to a ΔΣ-modulator (101) and converted to a plurality of n bit digital signals (111) by the ΔΣ-modulator (101). The plurality of n bit digital signals are converted to mismatch shaped m number of digital signals by a post-filter (112). The m number of digital signals are converted directly to analog audio by inputting to a speaker drive circuit (103) and driving s number of drive elements (104). The ΔΣ-modulator (101), the post-filter (102), and the speaker driving circuit (103) are structural elements of a digital speaker apparatus.